chocolate toffee cookies

INGREDIENTS

• 1/2 cup all purpose flour
• 1 teaspoon baking powder
• 1/2 teaspoon salt
• 1 pound bittersweet (not unsweetened) or semisweet chocolate, chopped
• 1/4 cup (1/2 stick) unsalted butter
• 1 3/4 cups (packed) brown sugar
• 4 large eggs
• 1 tablespoon vanilla extract
• 5 1.4-ounce chocolate-covered English toffee bars (such as Heath), coarsely chopped*
• 1 cup walnuts, toasted, chopped
• Flaky sea salt for sprinkling (optional)